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Task Vehicle Availability Rate (TVAR)

The Army's truck capability is organized in typical military unit configuration: companies, platoons, and detachments. Each truck unit has a doctrinal capability to move military cargo. One of the critical factors determining a truck unit's capability is the Task Vehicle Availability Rate (TVAR). The TVAR applies to all types of truck units, including the medium truck companies that transport general cargo and ammunition in the corps and at echelons above corps (EAC).

Trucks are the vehicles that a unit uses to perform its cargo-hauling missions. Not included in this definition are the unit's command and control or administrative vehicles. The number of trucks in a unit varies with the type of truck unit. For example, a medium truck company (cargo) has 60 tractor-semitrailer combinations (up to 2 1/2 times as many semitrailers as tractors). The number of tractors is the limiting factor in calculating truck unit capability. A medium truck company (palletized load system [PLS]) has 48 PLS trucks and 48 PLS trailers.

Load is the average weight a truck carries on a single trip. This is usually expressed in terms of tons, which refers to the standard short ton of 2,000 pounds. Other common measures of load include containers (in numbers) or gallons (of bulk liquid cargo).

Trip refers to a round trip (from origin to destination and return) performed by a single truck. In doctrinal line-haul operations (around the clock), each truck makes one trip per operating shift (12 hours), or two trips per day.

TVAR is the average percentage of task vehicles that reasonably can be expected to be available to accomplish the mission. It accommodates all the factors that can prevent a truck from transporting cargo, such as maintenance deadline or lack of a driver. The TVAR is never interpreted as a performance standard or goal. It is related to, but not the same as, operational readiness and operational availability. If the TVAR for a specific type of truck unit is 80 percent, on some days more than 80 percent of the trucks will be available to carry cargo; on other days, less than 80 percent will be available. But, over a period of time, 80 percent will be the average TVAR for that type of unit.

Using the terms defined above, the daily capability of a truck company can be expressed algebraically as:

Capability = Trucks TVAR (Load Truck) (Trips Truck Day)

This is the basic algorithm for computing a truck unit's capability. It determines the capability statement in part I of all truck unit tables of organization and equipment (TOE's). The algorithm highlights the TVAR's significance; however, it is one of only four critical factors that determine the capability of truck units.

Evolution of the TVAR

The TVAR concept has an interesting history dating back to the first military use of motorized vehicles by the Allied Expeditionary Forces in World War I. One of the earliest quantitative references to the TVAR is in a World War II manual. It states that planners should "assume that 70 percent of the fleet vehicles can be considered operating vehicles." This manual also attributes vehicle nonavailability solely to maintenance-related issues.

The TVAR percentage varied over time until the late 1960's, when it was established at 75 percent "for advanced planning" purposes. This value remained the Transportation Corps' standard until 1992.

In recent years, "downsizing" has become a simple fact of Army life. Resource reductions have led to precise scrutiny of the factors that drive force structure requirements. Because the TVAR is used to determine truck unit capability and truck company requirements in the Army, it also has been scrutinized. In response to repeated challenges to the long-standing, but analytically unsubstantiated, 75 percent TVAR, the commander of the Army Combined Arms Support Command (CASCOM) at Fort Lee, Virginia, directed in May 1992 that the TVAR for all truck companies be increased to 90 percent. This value was not analytically substantiated either. In fact, for over 50 years, the TVAR has been derived from "theater experience." The 90 percent TVAR simply reflected more recent perceptions of "theater experience."

In September 1994, the Army Chief of Transportation, Major General David A. Whaley, requested the Training and Doctrine Command (TRADOC) Analysis Center-Fort Lee (TRAC-Lee) to analytically determine the TVAR. TRAC-Lee used the extended combat sustainability (ECS) model developed by the Army Materiel Systems Analysis Agency (AMSAA) at Aberdeen Proving Ground, Maryland, to analyze the TVAR. ECS is a repair shop simulation model designed to perform relatively quick comparisons of candidate systems over a sustained period of time. It is sufficiently responsive to permit agile analysis and flexible enough to permit sensitivity analyses of the various components of the TVAR.

Model Parameters

As configured for this study, the ECS model has a number of limitations and internal functions that impact TVAR analysis. Two of its limitations are particularly important: the model does not allow drivers to repair trucks in the field (it focuses on repair facilities), and it does not accommodate combat loss or damage to trucks. Also, it always generates optimistic TVAR results. The model uses the following parameters-

MMBOMF: mean miles between operational mission failures. This measures the frequency (in miles) at which a particular truck experiences any incident or malfunction that prevents it from performing a designated mission-essential function.

Drivers: the number of drivers in the unit who are available to drive task trucks. The number is prescribed in AR 570-2, Manpower Requirements Criteria (MARC), and, for most truck companies, equals 2 drivers per truck. Each driver works one 12-hour shift in each 24-hour day. When a truck goes into organizational maintenance, its drivers go with it; but if a truck goes to direct support or higher maintenance, its drivers are available to drive other trucks in the unit.

Mechanics: the number of mechanics available (at organizational and direct support levels) to maintain task vehicles. These data come from the Army MARC maintenance data base.

Part delay time: the average waiting time, in hours, if a required part is not immediately available.

Mission profile: doctrinal line-haul operations. In line haul, each truck makes one round trip per operating shift. The one-way distance is determined by mission, enemy, terrain, troops, and time available (METT-T) but, for planning purposes, is usually considered 90 miles. Each truck operates for 10 hours of each 12-hour shift for a total of 20 hours of rolling time per day. Drivers perform operator maintenance and services, and the trucks are loaded and unloaded during the 4 hours of nonrolling time per day.

The TVAR analysis subjected the transportation medium truck companies to multiple ECS model runs and averaged the results for each type of unit. The chart at the bottom of page 22 summarizes the results.

Interpreting the Results

Using the average TVAR shown (remember that it is optimistic) as a starting point, the results were subjected to various sensitivity analyses. Each analysis focused on one of the major factors used to determine the TVAR. Three of those factors are sensitivity of the TVAR to changes in MMBOMF; mission distance and duration; and driver availability.

MMBOMF changes. In the most sensitive case, increasing MMBOMF by 30 percent increased the TVAR by 2.9 percent; decreasing MMBOMF by 20 percent reduced the TVAR by 3.4 percent.

Mission distance and duration. Doctrinal line-haul operations assume a distance to which a truck can make two round trips per day. For planning purposes, this is 90 miles one way, or 180 miles per truck per operating shift, or 360 miles per truck per day. The TVAR is moderately sensitive to increasing mission distance. In the most sensitive case, increasing the distance by 30 percent, to 234 miles per truck per 10-hour shift, decreased the TVAR by 4.6 percent. If mission duration is increased from 10 hours to 12 hours per shift (operating each truck 24 hours a day for a total of 432 miles), the most sensitive case drops the TVAR by about 8 percent.

Driver availability. The MARC for drivers is 2 per truck. This means that, in line-haul operations, one driver drives for 12 hours in a day and the other drives for the other 12 hours; therefore, nonavailability of a single driver results in the loss of one shift for one truck. Like most companies in the Army, truck company TOE's are designed with three authorized levels of organization (ALO's). ALO 1 is fully capable; ALO 2 reduces the company's strength and capability to approximately 90 percent of full capability; and ALO 3 reduces strength and capability to approximately 80 percent of full capability. The chart at left (above) shows the impact of reduced strength levels on the TVAR. Reduced strength levels affect each type of unit's daily line-haul capability (in tons of breakbulk general cargo).

Most of the Army's active component truck companies and a sizable number of its reserve component truck units are structured at ALO 2 or ALO 3. Considering the TVAR's sensitivity to ALO, the impact of reduced strength levels on the Army's ability to sustain military operations becomes apparent.

The TVAR is a significant determinant of truck unit capability. TRAC-Lee's study provided the Army a set of analytically determined, TOE-specific TVAR's that can be used with confidence to calculate TOE capability statements. They are now being incorporated into transportation doctrine and into TOE's for truck units. Ultimately, TVAR's will be used to develop new allocation rules for Total Army Analysis, the Army's process for determining the force of the future.



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